Production of uniformly pill-resistant polyamide fibers



assists Patented Feb, 18, 1964- This invention relates to the productionof which are resistant to pilling and fuzzing in articles.

Fibers prepared from synthetic linear polyares have proved superior tonatural fibers in many respects and are particularly noteworthy fortheir increased durability. However, when fibers of staple length areemployed in many end-uses, such as in loosely-woven fabrics, certaintypes of carpets and the like, the finished a1 'ticle becomesunsatisfactory in appearance after short usage due to excessive pillingand fuzzing. Filling refers to the formation of little balls of fiber onthe surface of the finished article due to the entanglement of loosefibers. Less; well-defined fiber entanglements are called fuzz.

Effectively pill-resistant polyarnide fibers and a process for theirproduction have been disclosed by Matray Stine in US. Patent No.3,050,822 and in a continuationin-part thereof bearing Serial No.177,762, filed March 6, 1962. In those disclosures, the pill-resistantfibers have een described as having frequent spaced weal: spots theirlengths. The accumulation of pills fuzz in finished articles preparedwith such fibers is avoided by breakage of the anchoring fibers at theweak spots, which are characterized with respect to frequency andseverity by a value no greater than 0.80 for :3 ratio of Tl/TQ where Tis the average break tenacity in grams/ denier of a one-inch samplelength and T is the average break tenacity of rninirnun -length samples(Zero distance be tween the tester jaws). The fibers have also beencharacterized as to weak spot severity by a significant reduction inloop toughness to a value of from 227, preferably 2l5, and by areduction in molecular weight at the weak spots. They have been furthercharacterized as to weak spot severity, abrasion resistance and.durability by a value of at least 150 for the expression IvI.W.OG0

toughness therein where M.W. is the molecular weight of the poly amide.

The most important object of my invention is to 3 a simple andeconomical process for producing the p resistant polyamide fibersdescribed by Matray and Stine.

A further important objective is the provision of process variationswhich lead to the production of more uniform pill-resistant fibers.

These and other objectives are accomplished by continuously anduniformly applying an aqueous peroxide solution containing from 5-30% byweight of hydrogen peroxide to a pluralit of drawn polyamide filamentsas they advance to a continuous mechanical crimping opera tion whereinthe tow is crimped and excess peroxide solution squeezed out.Subsequently, the tow is steamed for a time sufficient to substantiallycomplete the reaction of hydrogen peroxide with the fiber. Preferably,the hydrogen peroxide sol fore the tow enters the crimper.

Where reported herein, loop toughness and tenc' y values are determinedas described by Matray and Etine.

*1 is applied by spraying just be- Example Polyhexamethylene adiparnideis prepared, melt extruded, and cold drawn in the conventional manner toform a 7900-filament tow. Filament denier of the drawn tow is 12. Thetow is crimped mechanically by passing it through a stutter box crimperwhere it is subjected to sufficient pressure to provide an average ofcrimps/ inch in the filaments. it is fed to the stutter box crimper at arate of 400 y.p.n1. As the tow enters the crimper, it is sprayed with a15% aqueous hydrogen peroxide solution at a rate of one gallon/minute.Excess hydrogen peroxide solution is squeezed out in the crirnper anddrained off for recirculation to the sprayer. The emergent tow contains,by analysis, 2.8% hydrogen peroxide based on the dry weight of thefiber. This crimped, peroxide-treated tow is placed in a rectangularcontainer, the bottom of which consists of a coarse screen to permitpassage of gases upwardly through the container. The container oftreated tow is then placed in an autoclave where a vacuum equivalent toinches of mercury is applied for 5 minutes. Steam at 36 p.s.i.g. (l34.5C.) is then passed upwardly through the mass of fiber for 50 minutes.The steam is supplied by perforated pipes located beneath the container,and the autoclave and container are provided with peripheral seals whichprevent the escape or" steam around the outside of the container. Bythis means, the steam is caused to pass upwardly through the fiber massin a uniform fashion to complete the reaction of peroxide with thefiber.

The steamed tow is then dried and cut to 4 /2 inch staple in theconventional marmer. By measurement, T is found to be 1.02 grid. and Tis 2.25 g.p. cl., giving a T /T ratio of 0.45. The loop toughness of thetreated fiber is 4 as compared to a value of 200 for the untreatedfiber.

Uniformity of the fiber, as measured by point-to-point variation in thetenacity of samples taken from the autoclave basket, is significantlybetter than that of fibers prepared by mping and subsequently applyingthe peroxide by spraying it on the fibers in a centrifuge. Theinterfilanient variation within the tow is also improved as compared totow treated by the centrifuge process, the coefficient of variationbeing 39% as compared to 49% for the centrifuge process.

When the staple is processed into yarn by the conventional woolen systemand a oz./sq. yd. plain velvetweave carpet is fabricated therefrom, itis found to be equivalent in pilling and fuzzing erforrnance to a woolcarpet of similar construction and has a durability 3 to 4 times that ofthe wool carpet.

The foregoing example illustrates the advantages of the process of thisinvention in the simple and economical production of fibers havingimproved uniformity relative to those produced in other practicablecommercial proc esses. In this respect, the previously disclosedcentrifuge process of Natray and Stine, although suitable and practicalfor large-scale, commercial production, is less desirable from thestandpoint of initial investment and cost of operation.

The peroxide solution may be added to the tow in any suitable fashionprior to crimping provided that the application is reasonably uniformand an excess of solution over that required to achieve the desiredlevel of tenacity and toughness is employed. Such an excess insures areasonably uniform distribution of solution over the fibers. Preferably,there should be very little delay between the application of peroxideand the crimping operation since it is desirable that most of thereaction take place after crimping to provide a desirable spot-weakenedproduct. As disclosed by Matray and Stine, the reaction tends to bepreferential to the crimp nodes, and, consequently, the yarn should becrimped during most of the reaction in order to provide the mostdesirable product. The preferred procedure is to spray the peroxide onthe tow as it enters the crimper. in this manner, the need for aseparate solution-removal step is avoided.

The conncentration of the hydrogen peroxide solution applied to thefibers should be in the range of 5 to 30% in order to achieve thenecessary weakening of the fibers while, at the same time, avoidingdegradation beyond the point of satisfactory utility. Preferably, theconcentration is in the range -20%. It will, of course, have to beadjusted in consideration of the amount of solution remaining in thefiber after the crimping step. This will depend to a considerable extentupon the pressure required to develop the desired crimp in the fiberalthough some control of the amount of liquid removed may usually beachieved by suitable adjustment of the crimper feed rollers.

In order to prevent premature decomposition of the peroxide, very purematerial must be used in preparing the aqueous peroxide solution and thematerials of construction for the equipment employed in handling thesolution must be carefully selected. Contamination with metal ions, e.g., copper, iron, manganese, chromium, lead and cobalt, should beavoided as these ions are known to catalyze a decomposition of hydrogenperoxide. The hydrogen peroxide used to make up the more dilutesolutions should be of good purity and should preferably containstabilizing agents (e.g., sodium stannate and sodium pyrophosphate)which inactivate small amounts of catalytically active substances. Themost suitable material for use in tanks and other containers is aluminumof high purity. Stainless steel (300 series) may be used for limitedcontact at room temperature if properly passivated. Parts which cannotbe fabricated from aluminum or stainless steel should be made of asynthetic resin, e.g., nylon or polyoxymethylene, or should be coatedwith a resin such as polyvinylchloride.

The only requirement relative to the crimper employed is that it be apressure type crimper designed for continuous operation. A conventionalstutter box crimper is satisfactory. Crimpers of this type are describedin U.S. Patents Nos. 2,311,174, 2,734,229, and 2,917,784. The crimpershould, of course, be made from corrosionresistant mate-rial and thematerials of construction should not be such as to contaminate theperoxide solution with undesirable metal ions as indicated above.

The steaming operation should be carried out in such a manner as toapply the steam as uniformly as possible to all the fibers. Toaccomplish this, the steam is preferably forced through the fiber massby positive pressure as described in the example. The temperature andtime in the steaming operation should be adjusted to substantiallycomplete the reaction of the peroxide with the fiber. Preferably, thesteaming period should be held to the minimum necessary to achieve thatresult since excessive heating may result in discoloration of the fiber.Preferably, the steam temperature should be held below 145 C. and theoptimum range is 125-140 C.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. In a process including the steps of drawing nylon filaments, crimpingthe drawn filaments in a stutter box and cutting staple from the crimpedfilaments, the added steps of: spraying an aqueous solution of hydrogenperoxide on the filaments as they advance to the stufier box and heatingthe crimped filaments, the time-temperature 4 relationship of theheating step being such as to complete the reaction of hydrogen peroxideand nylon.

2. In a process including the steps of drawing nylon filaments, crimpingthe drawn filaments and cutting staple from the crimp'ed filaments, theadded steps of: spraying an aqueous solution containing 5-30% by weightof hydrogen peroxide on the filaments as they advance to be crimped,gathering the crimped filaments in a closed container and steaming thefilaments in said container, the time-temperature relationship of thesteaming step being such as to complete the reaction of hydrogenperoxide and nylon.

3. In the production of staple, the successive steps of: treatingcontinuously advancing nylon filaments with an aqueous solution ofhydrogen peroxide; passing the treated filaments to a stuffer boxwherein they are crimped under pressure; exposing the crimped filamentsto a vacuum atmosphere; heating the filaments, the time-temperaturerelationship of the heating step being such as to complete the reactionof hydrogen peroxide and nylon; and cutting staple from the filaments.

4. In the production of yarn, the steps of: treating drawn nylonfilaments with an aqueous solution of hydrogen peroxide; crimping thetreated filaments in a stufier box; and heating the crimped filaments.

5. The process of claim 4 wherein, in advance of the heating step, thecrimped filaments are exposed to a vacuum atmosphere.

6. In a process including the steps of drawing nylon filaments, crimpingthe drawn filaments in a stuffer box and cutting staple from the crimpedfilaments, the added steps of: spraying an aqueous solution of hydrogenperoxide on the filaments as they advance to the s-tufier box andheating the crirnped filaments, the time-temperature relationship of theheating step to the concentration of peroxide in the crimped filamentsbeing such as to produce weak spots in the length of each filament andto reduce its loop toughness to a value of from 2-27.

7. The process of claim 6 wherein the concentrationtime-temper-aturerelationship of the treating-heating steps is such as to produce weakspots in the filament, predominantly at crimp nodes, said weak spotsbeing characterized as to frequency and severity by a value of less than0.80 for the ratio T T o where T is the break tenacity in grams/ denierof a one-inch sample and T is the break tenacity of a Zero-lengthsample, said filament being further characterized by a value of at leastfor the expression toughness where M.W. is the molecular weight of thepolyamide in the filament and by a toughness of from 2-15.

References Cited in the file of this patent FOREIGN PATENTS 1,154,495France Apr. 10, 1958 1,024,482 Germany "Feb. 20, 1958 1,033,175 GermanyJuly 3, 1958 1,034,133 Germany July 17, 1958

1. IN A PROCESS INCLUDING THE STEPS OF DRAWING NYLON FILAMENTS, CRIMPINGTHE DRAWN FILAMENTS IN A STUFFER BOX AND CUTTING STAPLE FROM THE CRIMPEDFILAMENTS, THE ADDED STEPS OF: SPRAYING AN AQUEOUS SOLUTION OF HYDROGENPEROXIDE ON THE FILAMENTS AS THEY ADVANCE TO THE STUFFER BOX AND HEATINGTHE CRIMPED FILAMENTS, THE TIME-TEMPERATURE RELATIONSHIP OF THE HEATINGSTEP BEING SUCH AS TO COMPLETE THE REACTION OF HYDROGEN PEROXIDE ANDNYLON.